The present invention relates to radiation curable compositions suitable for use in the field of hot melt ink-jet printing and other applications.
Hot melt inks for use in ink-jet printing are compositions in which a dye or pigment is admixed with a vehicle which is essentially solid at room temperature but liquid at an elevated temperature at which print heads operate. The main advantage of hot melt inks over ink-jet inks which are liquids at room temperature, is that they solidify rapidly upon contact with the substrate. They are solid at room temperature and thus give a print quality which is essentially independent of the nature of the substrate. Moreover, independent temperature control of the substrate allows control of droplet spreading, again essentially independent of the properties of the substrate. This enables a superior print quality to be achieved than is obtainable with the liquid inks.
Current hot melt inks rely on solidification upon cooling to provide integrity of the print. Therefore, the durability of prints produced by the conventional kind of hot melt system is less than would be optionally desired in some applications.
Hot melt ink-like compositions are also used for modelling prototypes of articles of manufacture. A three-dimensional design produced on a computer aided design (CAD) system is used to control a hot-melt system which is used to xe2x80x9cprintxe2x80x9d a hot melt composition in layers to build-up the complete prototype. The compositions used for this application need to be very hard at room temperature.
On the other hand, radiation-curable ink-jet inks are free-flowing liquids at room temperature. They spread rapidly on contact with the substrate until radiation curing causes xe2x80x9csettingxe2x80x9d of the ink droplets. As mentioned above, the print quality with such inks is substrate dependent. It is difficult to control the degree of droplet spread and prevent inter-droplet smear.
JP 06200204 discloses a radiation curable ink for an ink jet printer which is solid at room temperature. It comprises from 10% to 30% by weight of a radiation-curable prepolymer and monomer and from 70% to 90% by weight of a wax and resin thickener.
New forms of hot melt ink formulation have now been devised which achieve benefits over both hot melt ink-type compositions and radiation curable ink-jet compositions.